According to the Oregon Department of Agriculture, the 18 pesticides contain the active ingredient dinotefuran.

"I have directed the agency to take this step in an effort to minimize any potential for additional incidents involving bee deaths connected to pesticide products with this active ingredient until such time as our investigation is completed and we have more information," said ODA Director Katy Coba in a statement. "Conclusions from the investigation will help us and our partners evaluate whether additional steps need to be considered."

The restricted pesticides are used professionally and by homeowners. But pesticides with dinotefuran that are used for flea, ticks, home ant and roach control are not affected by the ban, ODA says. The agency is only concerned about uses of the pesticides that could affect pollinators.

The restriction is for six months and takes effect immediately. After that time, ODA says it will have determined if the pesticides that killed the bees were used improperly.

A private contractor sprayed about 55 trees with Safari in the parking lot of the Wilsonville. The city of Hillsboro sprayed about 200 trees with the same pesticide in March. But bumblebee deaths were only reported at one tree.

The trees were sprayed to control aphids.

The trees in Wilsonville and the one in Hillsboro were covered with netting to protect bees from being poisoned.